Conventionally, there is proposed a name retrieving method of entering an institution name and retrieving an institution that matches the entered name. For example, as shown in FIG. 3, an institution matching the name “AICHIKEN” is retrieved from index data for the name retrieval. The index data stores only information needed for the name retrieval. The other detailed information about institutions is stored in detail data. The index data stores an address (or memory address) of the detail data. The detail data can be referenced to from the index data. The index data also stores administrative JIS codes, area codes, and type codes. These pieces of data are used to narrow a range of many matching institutions according to areas and the like. On the other hand, the detail data is stored in accordance with mesh numbers assigned to meshes as disclosed in JP-A-2000-293099 (U.S. Pat. No. 6,556,919), for example.
When an entered name matches many pieces of associated institution data, any retrieval range may be specified to retrieve institutions corresponding to the specified retrieval range. The index data for name retrieval does not contain positional information about institutions. Therefore, the detail data needs to be accessed to extract institutions having the corresponding coordinates. However, too many accesses to the detail data disable an efficient access. As a result, an overall retrieval process takes a long time.
If the index data for name retrieval stores the positional information about institutions, the size of the index data itself increases. This also increases the number of acquisitions of the index data for name retrieval, thus degrading the performance.